This is the first-cut technical drawing for the second injection mold part. The first, of course, is the hemispherical dome with the cylindrical section below (the skirt). I haven't yet re-drawn that, but we want to get the center of the hemisphere centered on the same geometrical center as that of the small hemispherical dome of the Dorne-Margolin antenna element. The height of the cylindrical sidewall will be specified such that both the tall and short dome models will be so centered.

So, this drawing supersedes the sketch drawing I sent by FAX that had a half-circular part. I since talked that over with Mark H. and found it would not work as well in production, since even a semi-circular part would need to use a full sized block of metal so that it could be sprued through the center. So, since the half-base is not a major design advantage or requirement, we will now go ahead and make the base-ring assembly in one circular part. The north-south oriented rib is twice as thick so that if we ever need to remove and replace one in the field, we can bandsaw cut one in half along this line, drill a couple of holes, and bolt/glue the part back together while leaving the adaptor in place.

The mold for this part should be possible to make for about $25-30K. It will make the former 'ring' part and the former 'base plate' part by injection molding off of a single mold, in two separate production runs. Between the times of the two runs, a metal rim can be inserted into one half of the mold, blocking off the 'base plate' portion, so that only the ring (for the short dome) will be made in the second run, for example.

Also, there are a couple of advantages according to Mark H. of this design over the previous for the hemispherical part. First, by avoiding a thickened wall around the base, differential shrinkage will be less. This will obviate the need for a drying (shrinking) rack part. Also, it means that a lower tonnage press may be required. It will also be cheaper to machine the mold for the part now (trade-off with cost of machining the mold for the base/ring assembly).

Other considerations:

• 1. For the short dome rings, the holes would be drilled through within the 'insert boss' and would have a 0.266" diameter, smooth-walled hole so that the mounting screws slide on through (the holes in the antenna's outermost choke ring are threaded). Probably we need to have another separate drawing to show the difference in molding and in secondary operations for the 'tall dome ring/base assembly' versus the 'short dome with ring assembly.' For the short dome, I think perhaps that we should have every 'even' hole be an insert, and every 'odd' hole go on through. This would allow the short dome to be attached to the ring using the insert set, and allow the dome/ring assembly to be attached to the antenna with the set of holes that are drilled through. I also think we should standardize these screws so that they are security screw heads (torx) and all have the same heads. This issue recently came up with the same type of situation for the attachment of the DM element into the choke ring assembly. The importance of this is so that there is never any question about whether SCIGN's short dome screws are different or same as someone else's - we can avoid that ambiguity just by specifying the screws at the outset as part of the drawings, and sticking with that spec. Needless to say, when we provide the short domes to others (e.g. GPS manufacturers), we should provide a set of the proper screws with each dome.

• 2. The hole to be drilled in this same boss, but for the tall dome model, with base plate and ring assembly, needs to fit a standard insert for ultrasonic welding. In product literature I have from Tri-Star Industries, Inc., and assuming we plan to stick with the 6-32 threaded torx head we specified previously, I see we need to have a hole depth of >0.30". We should probably use a tapered hole (8 degree) and the boss diameter should be at least 0.412" for the inserts spec's I am looking at. These numbers are for their 'long' insert, yet are still shorter than the threaded holes Steve had in the earlier drawings.

• 3. In the previous drawings, the torx screw heads were to come in from the base plate, with a 0.1" countersunk hole for the screw head. Now, we'll be coming in from the side (through the hemisphere). If we have that same 0.1" countersink, it leaves only 0.025" of plastic there. Is that enough or are we in trouble with this? I thought of wrapping that outermost 'ledge' up around the outside wall of the dome edge, and we could do that. John G. doesn't much like having that lip there at all, and we could have just a ledge without the outermost rim there. I thought it would help hold the hemisphere in the correct shape even if it gets hit very hard, and take some pressure off the screws if and when a sharp blow to the dome occurs.

Same drawing, in several different file formats:

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